Window sashes, door panels, and window and door frames often are constructed from several elongated members, or “lineals,” such as, for example, members that surround panes or panels of glass, wood, metal(s), plastic(s), insect screens, etc. Horizontal lineals are commonly referred to as rails, while vertical lineals are commonly referred to as stiles. Although rails and stiles can be made of wood, windows and doors constructed from solid wood can be expensive and require special maintenance and care. Materials, such as plastics, vinyl and composites of wood and resin, compare favorably with the aesthetic beauty of solid wood while offering benefits such as economical pricing, reduced maintenance, and easy installation.
The benefits and relatively low maintenance required for plastics, vinyl, or composite materials make such materials an attractive choice for rails and stiles and other window sash, door panel, or window and door frame components. When forming rails and stiles, these materials typically are extruded into an elongated member (which could be a lineal member) having a cross-section adapted to receive glass panes or solid panels formed from other materials. The rails and stiles are cut to length and fabricated according to the dimensions of the window or door, and are then assembled typically by joining the rails and stiles together at their ends with, for example, mitered corner joints, end butt joints, or mortise and tenon corner joints. As a result of the extrusion process, the rails and stiles typically have an internal cavity. Members with cavities, such as extruded window and door parts with cavities extending the entire length thereof, generally consume less material and are lighter in weight than solid parts having equivalent dimensions. However, forming corner joints between rails and stiles with internal cavities that have the requisite strength, structural integrity, and weather resistance while maintaining a clean aesthetic look is difficult. Although it is known to join the rails and stiles together at their ends with internal inserts, such as complex corner keys, or by hot plate welding or sonic welding, these techniques can exhibit problems and shortcomings. In particular, forming a sufficiently robust attachment between internal inserts such as corner keys and members with cavities can be difficult, especially when the external appearance of the structural members is critical.
Parts used to join members also can require large inventories of similar, but not equivalent, items, such as corner keys for example. Corner keys are used in several situations, including situations where different members are to be joined. Often these different members have different internal cross sectional profiles, with each profile typically requiring a custom shaped corner key, leading to large inventories of corner keys and potential confusion as to which corner key to use for a particular member. This situation can be further complicated by the occasional need to join dissimilar members, for which an appropriate corner key may never have been made, or can be further multiplied by the need to join members at different angles.